This invention relates to data communication systems and more particularly to methods of polling and transmitting data to a large number of terminals via a high speed transmission medium.
Communications between individuals or groups in today's world occur in a variety of ways, each of which involves a particular medium. Well-known mass communications media include radio, television, telephone, motion pictures, mail or correspondence, newspapers, and magazines. With the exception of the telephone and mail, these media are primarily one-way communication systems from which the general public may receive information, but cannot readily communicate back in the same medium. Moreover, the communications medium of mail and telephone each possess shortcomings when mass communications is desired. A variety of polling schemes are generally known in the art. In this context, polling is described as a process of addressing one of a number of remote stations or receivers connected via a common data link to a central control station by signals from the central control station. In these prior art polling systems, all of the various remote stations connected to the transmission link receive this address or polling signal, but at any given time, only one of these remote stations or receivers is designed to recognize the address or polling signal received as his own. Upon recognition, the remote station is enabled to transmit over the data link any information which it may be passing to the central control, or alternatively, receive information transmitted from the central station. In the usual polling scheme, each remote station is invited, in turn, to send inbound traffic by polling signals sent out by the central control station. A given remote station may, upon the receipt of a polling signal do, in general, one of two actions: it may begin to send any messages which it has awaiting the opportunity for transmission, or it may send back an answer code indicating that it has no traffic for transmission at that time. The central station must wait until the addressed or polled remote station responds or acknowledges the poll before a new polling signal can be initiated. During this waiting period, there can be no communications with any other terminal. If there is no priority scheme, each remote station or terminal will be polled once before any terminal will be polled again. Thus, as the number of remote stations or terminals connected to the link increase, a proportionate increase in response time will occur.
Today, however, with the increased emphasis in large scale data communications in such applications as point of sale systems, there is an increasing requirement for a large number of terminals to have access to a central data base. At the same time, it is vital that response time be at a reasonable level.
Therefore, it is a primary object of this invention to provide an improved data communications system.
Another object of this invention is to provide an improved communications system which will permit large numbers of remote terminals to be connected to a common transmission link without an appreciable increase in response time.
A further object of this invention is to provide a polling scheme for use in a data communication system having a large number of remote terminals.
A still further object of this invention is to provide a scheme for polling concurrently a large number of remote terminals connected to a common transmission link.